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    <title>Document</title>
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    <h1>哈哈哈</h1>
    <p>QAQ</p>
    <p>123</p>
    <script>
        let a = 10;
        a = 20;
    </script>
    <div>a</div>
    <script>
        let a = 10;
        a = 30;
    </script>
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